Twenty healthy male adult volunteers participated in this study. The volunteers appeared at the testing location, having refrained from eating and drinking for six hours. All the volunteers were monitored with electrocardiogram (DII and V1 derivation), pulse oximetry (SpO2), non-invasive average arterial pressure and bispectral index (BIS). Oxygen under 2.0 L.min-1 nasal catheter was used and the left antecubital vein was punctured and connected to the venous catheter filled with propofol (Propovan® - Cristália Laboratório Ltda).